硅锗合金纳米粒子的合成与表征-solarbe文库

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Synthesis and Characterization of Silicon-Germanium alloy Nanoparticles in Nonthermal Capacitively-Coupled Plasmas Jatin Rath Md. Seraj Uddin Ansari, C Vijayan Indian Institute of Technology Madras, India jkriitm.ac.in, J.K.Rathuu.nl SNEC 13th 2019 International Photovoltaic Power Generation and Smart Energy Conference June 3-5, 2019, Shanghai, China Contents Introduction/Motivation Experimental Results and Discussion Conclusion References Introduction/Motivation § SiGe alloy nanoparticles NPs are very promising candidates for solar cell applications. § The size dependent optical and electronic properties and bandgap engineering due to quantum confinement in SiGe NPs make them more favorable for quantum dot based Tandem Solar Cells. § However, these NPs suffer from Ge segregation and also face Ge diffusion from core to the shell to minimize the dangling bonds in case of hydrogen free nanoclusters. § To tackle these challenges a good process control is needed during NPs’ growth. § A nonthermal plasma CVD technique used in this work for synthesis, gives good monodispersed, freestanding gas phase NPs of device quality. Experimental Fig Schematic of VHF PECVD reactor. ref J. Phys. D Appl. Phys., vol. 48 ,p. 375201, 2015. § Frequency 60MHz § Power 150 W § Pressure 0.8 mbar § Gas flow ratio R i.e, RSilane/Germane § Dilution Ar/H 2 gas or H 2 alone. Sample ID Gas Used Flow ratio RSilane/Germane Plasma mode S1 Ar H 2 SiH 4 GeH 4 25 sccm 25 sccm 4 sccm 2 sccm R2 CW S2 Ar H 2 SiH 4 GeH 4 25 sccm 25 sccm 4 sccm 4 sccm R1 Pulse 250 msec S3 Ar H 2 SiH 4 GeH 4 25 sccm 25 sccm 4 sccm 4 sccm R1 CW S4 H 2 SiH 4 GeH 4 50 sccm 4 sccm 4 sccm R1 CW SiGe NPs synthesis VHF PECVD reactor The four samples prepared at different conditions are given in table CW plasma Pulsed plasma Results and Discussion Raman Spectroscopy Si-Si 480 cm -1 Ge-Ge 275 cm -1 Si-Ge 390 cm -1 Si-Si 469 cm -1 Si-Ge 391 cm -1 Ge-Ge 285 cm -1 Si-Ge 390 cm -1 Ge-Ge 276 cm -1 Si-Si 474 cm -1 Si-Ge 389 cm -1 Si-Si 474 cm -1 Ge-Ge 280 cm -1 a b c d The existence of TO Si-Ge Raman peaks in spectra conform the SiGe NP formation. There is a shift in Si-Si Raman peak in these spectra, this is due to heavy Ge atom incorporation in Si lattice during alloy formation. Ar H 2 SiH 4 GeH 4 25 25 4 2 sccm Ar H 2 SiH 4 GeH 4 25 25 4 4 sccm Ar H 2 SiH 4 GeH 4 25 25 4 4 sccm H 2 SiH 4 GeH 4 50 4 4 sccm R2 R1 R1 R1 CW CW CW Pulse 250 msec Raman Spectrosopy Continue ref J. Appl. Phys. 114, 134310 2013 The Ge content in SiGe NPs from Raman spectra a The shift in Si-Si peak Due to Ge atom incorporation and not from the shift due to Nano-crystallite size The peak shift value is very nominal from nano-crystallite size y520-70x y Si-Si TO phonon Raman peak position x is the fraction of Ge in SiGe NP Sample ID S1 S2 S3 S4 Ge content 0.57 0.66 0.66 0.73 The Ge content of Si 1-x Ge x in different samples Sample ID Flow ratio R in reactor R in SiGe NPs S1 2 0.75 S2 1 0.51 S3 1 0.51 S4 1 0.37 Comparison of RSilane/Germane in CVD chamber and in SiGe NPs TEM image images are from sample S1. a b d c a Nicely dispersed NPs of size around 20nm quantum confinement b HRTEM image of NPs, shows lattice fringes in NPs proving the crystalline nature c Conforms crystalline nature from SAED image d Area EDS spectrum, shows the presence of Si and Ge in sample and the intensity ratio of Si and Ge peak also corresponds to the R. EDS Mapping from HAADF-STEM Image § The EDS mapping image clearly shows that the Si and Ge atoms are randomly distributed in NPs and so it form a homogeneous alloy. § The surface atom are getting oxidized and forming and oxide shell layer on NPs. Dark I-V Characteristics of SiGe using cAFM Dark I-V characteristics study for S4 sample in cAFM mode. Derivative of current is plotted w.r.t applied voltage. The band gap calculated for nanoparticle is E g 1.88 eV. Conclusion § The SiGe NPs synthesized in VHF CVD reactor § good process control and the particle size measured in TEM is in accordance with the quantum dots. § Raman spectra shows higher incorporation of Ge in NPs with H 2 dilution than pure ArH 2 dilution. § Si/Ge value in NPs is lower compared to R value Silane to Germane ratio CVD chamber. § Si and Ge atoms in NPs are randomly distributed and it conforms the homogeneity of alloy NPs and show no sign of segregation of Ge in NPs. 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